This invention relates to a method for repairing defects in gas turbine engine components and, more particularly, to utilizing a protective coating to resist inter-granular attack during chemical cleaning.
Conventional gas turbine engines include components such as high and low pressure turbine vanes that operate for extended periods of time under relatively harsh conditions. Under such conditions, the gas turbine engine components may incur damage from erosion, creep, and high cycle fatigue that results in defects such as cracks. Typically, the defects can be repaired to extend the service life of the gas turbine engine component.
Conventional repair methods include cleaning the defect to remove oxidation and particles that may hamper the repair. After the cleaning, a braze material such as a braze filler powder is applied near the defect. The gas turbine engine component is then heated to melt the braze material and fill in the defect portion.
Conventional cleaning processes include using hydrogen fluoride gas to reduce oxidation on the defect surface and transform undesired particles into volatile fluorides that are then carried away by hydrogen gas. Disadvantageously, the hydrogen fluoride gas preferentially attacks grain boundaries of a metallic microstructure of the gas turbine engine component, which may undesirably weaken the gas turbine engine component, lead to unsuccessful repair, and result in scrappage of the component.
Accordingly, there is a need for a method of cleaning gas turbine engine component defects while minimizing the possibility of inter-granular boundary attack.